The term “desiccator” commonly refers to two types of equipment and ranges of applications.
Desiccator drying enclosures use vacuum or desiccant, sometimes in conjunction with a fan, to remove moisture adsorbed into the surface layer of a sensitive sample. These enclosures are typically fairly small cylindrical or round glass vessels and are commonly used in life science laboratories to dry biological or pharmaceutical samples.
Desiccator cabinets are typically larger units, often with multiple chambers, used to prevent moisture exposure during storage of sensitive parts. Because storage applications must allow periodic parts access, desiccator cabinets typically include one of more doors and rely either on a desiccant material (regenerating silica gel or molecular sieve) or nitrogen purging to maintain dry conditions.
A purge of purified nitrogen is generally preferred in a large desiccator cabinet because such systems achieve a uniformly low-humidity storage environment more quickly than desiccant-based systems, particularly where ultra-low RH levels are required. Nitrogen can be fed into multiple locations in a large cabinet, often using a rear plenum as a distribution chamber. A mixing fan increases humidity uniformity inside the cabinet and promotes moisture dilution. Nitrogen-purged desiccators also prevent contact with oxygen, making them ideal for anaerobic applications.
Desiccant-based systems are preferable in facilities that lack a nitrogen source. However, because desiccant requires a periodic regeneration (heating) cycle, these desiccators cannot provide continuous moisture protection unless equipped with a redundant desiccant module. They are also typically unable to provide ultra-low humidity levels and require a longer RH recovery time when the cabinet is exposed to moisture.
RH recovery time is the time required to recover a low relative humidity set point when an access door is opened to part retrieval.
The acceptable RH set point depends on industry and application. Many semiconductor and optical sensing devices feature electronics that require a storage environment of less than 10%RH and are degraded by exposure of just a few minutes to moisture substantially above this level. Unfortunately, desiccators can require up to an hour to retain a 10%RH set point, particularly if ambient humidity is very high. If a door is opened again before set point is attained, parts may be exposed to unacceptable moisture levels for hours!
For such critical applications, Terra provides a number of high-efficiency nitrogen-purged desiccators, including the IsoDry line, which ensures RH uniformity and fast recovery time. In large, multi-chamber desiccators, Terra’s NitroPlex system even performs humidity monitoring and control in each chamber independently.
Improved low-RH recovery also reduces nitrogen costs.
Equipped with an automated gas control system, such as Terra’s Dual Purge and NitroWatch controllers, desiccators consume on average less than five cubic feet of nitrogen per hour, allowing a single 5’ pressurized liquid nitrogen tank to operate a large cabinet continuously for 2-3 days, depending on frequency of access and recovery time.
To eliminate dependence of nitrogen tanks, Terra offers Nitrogen Generators that produce up to 99% pure nitrogen from compressed air.
Acrylic and other plastics bear a weakness known as hygroscopy. Plastic surfaces naturally accumulate liquid molecules through adsorption, collecting moisture from the atmosphere that clings to its surface in a thin coat. While this might not present an issue for simple operations, it can be a challenge in moisture-sensitive applications.
A potential solution to the issue of humidity in small acrylic enclosures, such as glove boxes and desiccators, is the use of N2. Nitrogen is a dry gas commonly pumped into a chamber to lower the relative humidity and purge moisture to protect the materials inside. But constantly using a high flow of nitrogen gas can be expensive, and for critical applications requiring minimal humidity, compensating for an inherently moisture-attractive material can expend a ghastly amount of N2.
Regardless of the type of gas blowing across acrylic, air cannot dislodge moisture particles from its surface or prevent air and liquid molecules from permeating the glued edges of an acrylic chamber. For applications requiring the strictest low-humidity environments, stainless steel provides moisture-impermeable protection as well as corrosion and chemical resistance. And while stainless steel will protect the atmospheric conditions of the environment within the chamber, optional properties for steel types can provide further benefit.
The best resistance to humidity comes from electropolishing, a procedure that removes the top layer of the stainless steel surface. The process entails an electrochemical removal of metal impurities, including carbon, silica and free iron, and it leaves a highly reflective nickel and chromium surface. Electropolishing eliminates the grainy texture of standard stainless steel, which can retain trace amounts of moisture or pathogens that escape cleaning. As a result, the surface has a smooth texture at a microscopic level, and liquid molecules have nowhere to hide.
Terra manufactures desiccators specially configured for ICs, tote boxes, IC carrier reels, and other common microelectronics and electronics parts. Not only does desiccator storage eliminate damage that can be immediately detected, but it also prevents “dwell effect” – the more costly damage that doesn’t emerge until ICs or other components are installed in more complex assemblies, such as medical devices, that are more difficult to repair or replace.
Desiccators provide an inert gas environment for storing volatile chemicals. They can also be used for slow, controlled drying, and are available with customized heating capabilities. Use of a nitrogen or other inert process gas eliminates reactions caused by oxygen exposure.
The dry, inert environment inside a desiccator is ideal for storage of forensic materials, DNA samples, and biological cultures. Easy-clean BioSafe® stainless steel desiccator cabinets are ideal for use with materials that require a sterile environment.
Dry storage inhibits growth of organic contaminants and retards other chemical reactions that degrade pharmaceuticals.
Clean, dry storage environments for everything from archival records to archeological samples—call to discuss your application!